AD668SQ883B Analog Devices, AD668SQ883B Datasheet - Page 10

• Manufacturer Part Number: AD668SQ883B
• Description: The AD668 is an ultrahigh speed, 12-bit, multiplying digital-to-analog converter, providing outstanding accuracy and ...
• Manufacturer: Analog Devices

AD668
Nominal
Analog
Input
1 V
1.25 V
5 V
mode (Pin 22 grounded, input into Pin 21). Fine adjustment of
the gain is provided by both the AD586 external trim resistor
and the 100 Ω potentiometer in series with the reference input.
The resistive divider at the reference input will draw approxi-
mately 1 mA from the AD586, leaving plenty of driving current
for other loads in the system.
AC HOOKUP: 1.25 V AC FULL SCALE, 2.5 V DC FULL
SCALE
The circuit shown in Figure 12 allows separate setting of dc ref-
erence bias point on a 2.5 V scale and capacitively coupled ac
signal on a 1.25 V scale. The basic reference input is configured
in the 1.25 V mode (Pin 21 grounded, Pin 22 used as the refer-
ence input.) The 2.5 V dc range is achieved by using an external
Figure 11. AD586 Driving the AD668
0 V to 1 V
Unipolar
Unbuffered V
A
Unipolar
Unbuffered V
A
Pin 21 Grounded
Unipolar
Unbuffered V
A
Pin 22 Grounded
(See Figure 7)
IN
IN
IN
= Pins 21 + 22
= Pin 22
= Pin 21
OUT
OUT
OUT
–500 mV to +500 mV
Bipolar
Unbuffered V
A
Bipolar
Unbuffered V
A
Pin 21 Grounded
(See Figure 8)
Bipolar
Unbuffered V
A
Pin 22 Grounded
IN
IN
IN
= Pins 21 + 22
= Pin 22
= Pin 21
Table II. AD668 Topology Variations
OUT
OUT
OUT
OUTPUT LEVELS
–10–
0 V to –10 V
Unipolar
Buffered V
A
External Amplifier
(See Figure 10)
Unipolar
Buffered V
A
Pin 21 Grounded
External Amplifier
Unipolar
Buffered V
A
Pin 22 Grounded
External Amplifier
IN
IN
IN
= Pins 21 + 22
= Pin 22
= Pin 21
5k series resistor in the dc path. Note that because of the rela-
tively wide tolerance (± 20%) in the absolute value of the
AD668’s internal input divider resistors, substantial gain range
adjustment should be provided in the external series resistance.
DAC DRIVE: THE AD568 DRIVING THE AD668
The circuit shown in Figure 13 produces an analog output pro-
portional to the product of two digital inputs. The AD568 has
an on-board fixed reference and generates a full-scale output
voltage of 1.024 V (just as the AD668 does in its unbuffered
voltage output mode). This output voltage can be used to di-
rectly drive the AD668 in the 1 V reference input mode. Note
that in this case, the lower 410 codes of the AD568 are out-of-
bounds; they produce an undervoltage condition at the AD668
OUT
OUT
OUT
+5 V to –5 V
Bipolar
Buffered V
A
External Amplifier
Bipolar
Buffered V
A
Pin 21 Grounded
External Amplifier
Bipolar
Buffered V
A
Pin 22 Grounded
External Amplifier
Figure 12. AC Hookup
IN
IN
IN
= Pins 21 + 22
= Pin 22
= Pin 21
OUT
OUT
OUT
–1 V to +1 V
Bipolar
Unbuffered V
A
R
To I
Bipolar
Unbuffered V
A
Pin 21 Grounded
R
To I
Bipolar
Unbuffered V
A
Pin 22 Grounded
R
To I
(See Figure 9)
IN
L
IN
L
IN
L
(Pin 19) Tied
(Pin 19) Tied
(Pin 19) Tied
= Pins 21 + 22
= Pin 22
= Pin 21
OUT
OUT
OUT
(Pin 20)
(Pin 20)
(Pin 20)
REV. A
OUT
OUT
OUT